The spacecraft would drift away from any direction it was pointing over time without the stabilizing influence of at least three reaction wheels. They could probably maintain sufficient pointing accuracy by using thrusters, but the fuel for these would eventually be exhausted. They may get the balky wheel to work again, or may be able to bring the fourth reaction wheel back into service. It, too, gave trouble at one point and was turned off.

Another testament to the fact that space is a harsh environment. We may never know the exact cause of the failure as it could be anything from a flawed component to a micro meteor strike. Unfortunately they can only afford to provide limited redundancy as it adds to the launch weight and may never be called on to take over a function. Maybe we should invest in a robotic repair vehicle that could be launched with case specific replacement components. If the original vehicle had universal docking ports the repair craft could just dock, reroute the circuits and take over the function of the failed components. Just a thought. Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

i really hope they will send more crafts of those, successors. i think so far in the 21th century, it s the space program that paid the most and made the most huge step, more than any other space program.
and i wish this time we will try to get the most info on closest stars.
and i wish also they would add some kind of gear to record some broadbands (out of all earth interferences)

Following the apparent failure of reaction wheel 4 on May 11, 2013, engineers were successful at transitioning the spacecraft from a Thruster-Controlled Safe Mode to Point Rest State at approximately 3:30 p.m. PDT on Wednesday, May 15, 2013. The spacecraft has remained safe and stable in this attitude and is no longer considered to be in a critical situation.

"Nature" says it can't do much with 2 out of 4 gyroscopes not working. I wonder if the gyroscopes were not of the same quality of the gyroscopes of the Gravity Probe 2, probably much costlier because they were cryogenic.
Tullio

"Nature" says it can't do much with 2 out of 4 gyroscopes not working. I wonder if the gyroscopes were not of the same quality of the gyroscopes of the Gravity Probe 2, probably much costlier because they were cryogenic.
Tullio

Very different gyroscopes between those two spacecraft.

The gyroscopes on Kepler are 'control moment gyroscopes' that are spun up, spun down, and deliberately forcibly twisted around to 'push' the spacecraft in the opposite direction (by Newton's law of reaction) to deliberately orient the spacecraft. For Kepler, that is to keep a very steady orientation despite whatever buffet there might be from the solar wind and drift from radiation pressure.

The gyroscopes on Gravity Probe 2 are smaller and are designed to run in complete isolation to all outside influences. The Gravity Probe 2 spacecraft was a very clever design to not disturb the gyroscopes to allow any spacetime perturbations to be detected. As it turned out, there was horrendous complexity introduced into the measured results due to the small uneven forces from unwanted electrostatic charging! Gravity Probe 2 used the exhaust from the cryogenic helium boil-off as reaction thrusters to "fly" the space craft around the gyroscopes all without the gyroscopes coming into contact with any of the protective housing surfaces.

The multiple 'control moment gyroscopes' on the ISS are the size of big washing machines!

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I have been skeptical all along about some of the conclusions drawn from analyzing just a few pixels of light. Some of the stuff I've been reading and seeing on TV appears to be based on wishful thinking more than hard data.Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

In the field of planet hunting, Geoff Marcy is a star. The astronomer at the University of California at Berkeley found nearly three-quarters of the first 100 planets discovered outside our solar system. But with the hobbled planet-hunting Kepler telescope having just about reached the end of its useful life and reams of data from the mission still left uninvestigated, Marcy began looking in June for more than just new planets. He's sifting through the data to find alien spacecraft passing in front of distant stars.

I am not familiar with Berkeley U. structure and policies. But why does a Berkeley astronomer like Marcy seem to ignore the existence of SETI@home? The linked article mentions only the ATA telescope.
Tullio

Following months of analysis and testing, the team is ending its attempts to restore the spacecraft to full working order as the recent pointing test proved unsuccessful. We are now considering what new science research it can carry out in its current condition.